Start the game with the parameter "mostwanted.exe -cheats"
In the menu "Special Features" now should be an option CHEATS 
or you can open an console with the [~] key and type in the codes:

(0 = OFF, 1 = ON)

Code                      Effect
-------------------------------------
godMode <0/1>           - Toggle God mode for self.
godModeTeam <#>         - Toggle God mode for team.
noclip <0/1>            -  Toggle no clipping.
mw_failmission <0/1>    - Toggle mission failure.
mw_winmission <0/1>     - Toggle mission success.
mw_showhud <0/1/2>      - Toggle HUD.
mw_aiDisableThink <0/1> - Toggle AI.
mw_aiDisableAct <0/1>   - Unknown.
mw_givealllevels <0/1>  - Toggle level select.